Could be, but it's also not uncommon for plagiarists to try to stay on topic by copying something from earlier in the thread.
Having said that, I don't mind them getting a soft ban, just don't want to start the whole done-it-only-once-was-young-and-stupid excuse bingo

I would say, that it is not that case: there is no «plagiarism» mistake in situation when someone helps another one person in bounty (!!!) topic. If it would be a regular problem for him, then it could be so, but one time for 1803 posts copied answer of bounty manager to answer another user is not plagiarism at all. If we ask for more attributive quoting, well, it could be mistake of not enough attribution. Mistake, but not a crime, not a plagiarism. All my IMHO.
Unfortunately, we have caught bumping bots that just recycle the same questions and answers using various alt account to make it appear like different participants. When caught, the account that gave the answer could just state "they were being helpful."